A contractor undertook a contract to complete a part of a stadium in 9 months with a team of 560 persons. Later on, it was required to complete the job in 5 months. How many extra persons should he employ to complete the work?
∵ In 9 months, a part of stadium can complete by 560persons.
∴ In 1 month, the work can be complete by 9× 560 = 5040 persons.
∵ In 5 months, the work can be complete by 
68